Mechanical Governors

needle valve even though it has previously been done at the factory or repair facility. This adjust- ment must be made with the governor installed and controlling an engine with a load. If this is not done, high overspeeds and low underspeeds after load changes will result and the return to normal speeds will be slowed. Maintenance and repair of each unit must be in accordance with the manufacturer’s maintenance manual and the PMS. NOTE: When governor troubles are suspected, before performing any maintenance or adjustments, always disconnect the governor fuel rod end from the fuel control rack and ensure that there is no sticking or binding of the rack. This procedure is necessary to determine if the trou- ble is actually in the governor. The chart in table 3-1 lists some of the probable causes of trouble which are common to most hydraulic governors. This chart should be used for training purposes only; it must NOT be used to troubleshoot a governor. Always use the applicable manufacturer’s instruction manual for troubleshooting. Following are the definitions of the terms used in the chart. HUNT: A rhythmic variation of speed which can be eliminated by blocking the fuel linkage manually, but which will reappear when returned to governor control. SURGE: A rhythmic variation of speed always of large magnitude which can be eliminated by blocking the fuel linkage and which will not reap- pear when returned to governor control unless the speed adjustment of the load changes. JIGGLE: A high frequency vibration of the governor fuel rod end or engine linkage. Do not confuse jiggle with normal regulating action of the governor. Mechanical Governors Mechanical governors used in the Navy are generally of the spring-loaded flyball type. All mechanical governors have a speed droop. This means that as the load is increased at a constant throttle setting, the speed of the engine will drop or droop slightly, rather than remain constant. Consequently, mechanical governors are never used where absolute constant speeds are necessary. There are several types of mechanical gover- nors. Two of the most common types are used on GM 71 engines. One type, known as the constant-speed governor, is used on generator sets and is designed to hold the speed of the engine at a predetermined operating speed. The other type is similar in construction and is used primar- ily for propulsion engines. It has a throttle plate so designed that speeds intermediate between idl- ing and full speeds may be obtained by manual adjustment. The following description applies to both types of governors. Do note, however, that on the constant-speed governor, there is no buf- fer spring adjustment. In the idling speed range, control is effected by centrifugal force of two sets of flyweights (figure 3-15), large and small, acting against a light Chapter 3—ENGINE MAINTENANCE 121.22 Figure 3-15.—GM mechanical governor. 3-23